Polyethylenenaphthalate has very good stress- and heat-resistance. Its known preparation processes, however, have not been industrially profitable.
Polyethylenenaphthalate can be made from 2,6-naphthalenedicarboxylic acid which in turn can be made from 2,6 dimethylnaphthalene. Nowadays 2,6 dimethyl-naplthalene is separated from tar. However, in this way only small amounts can be obtained. Furthermore, the separation and purification are troublesome.
It has also been suggested that 2,6-dimethylnaphthalene is made from 1-(p-tolyl)-2-methylbutane and/or 1-(p-tolyl)-2-methylbutene by cyclization using different catalysts. The problem has especially been that in the reaction one obtains big amounts of different isomers, which are difficult to separate. Furthermore, the starting material easily polymerizes and degrades.
For instance, in the publication GB 1448136 there has been described the preparation of 1-tolyl)-2-methylbutane and/or 1(p-tolyl)-2-methylbutene using a Cr.sub.2 O.sub.3/ Al.sub.2 O.sub.3 -catalyst which has been poisoned by potassium. In the publication EP 430714 a catalyst composed of lead- and/or indium-oxide together with aluminium-oxide has been proposed.